1. Field of the Invention
The present invention relates generally to plastic molding processes and more specifically it relates to a method of manufacturing a screen device for permanent placement of a screen within a plastic structure.
2. Description of the Prior Art
Plastic molding techniques have been in use for years. The four most common methods of plastic molding are comprised of injection molding, blow molding, vacuum molding, and rotational molding.
Rotational molding offers many advantages over blow molding and injection molding. Rotational molding is well suited to producing parts that are seamless, fully or partially enclosed, and hollow with high side-wall strength and dimensional integrity. Rotational molding is superior to other molding techniques in the areas of cost reduction, economical runs and part size. Parts that are rotationally molded often provide an excellent, lightweight alternative to products usually formed of metal or fiberglass.
In rotational molding, liquid or powdered thermoplastic resin is formed inside a closed mold or cavity while the mold is rotating biaxially in a heating chamber. To obtain mold rotation in two planes perpendicular to each other (providing even distribution of the resin), the spindle is turned on a primary axis, while molds are rotated on a secondary axis.
Rotational molding (also popularly known as xe2x80x9crotomoldingxe2x80x9d) is best suited for large, hollow products requiring stress-free strength, complicated curves, a good finish, a variety of colors, comparatively short runs (flexible schedule), very long production runs (less costly), and uniform wall thickness. The process has been used for products such as water tanks, storage tanks, industrial containers, outdoor chairs and benches, road barriers, portable outhouses, modular bathrooms, garbage cans, telephone booths, boat hulls, light globes, ice buckets, appliance housings (carpet and vacuum cleaners), and toys. The technique is applicable to most thermoplastic but is most widely used with polyethylene.
There are essentially six basic steps in rotational molding; mounting the tool, loading resin, molding and curing, cooling, unloading the part, and final finish. First, tools are mounted on large spindles that will rotate during the heating process. Second, liquid or powdered plastic is loaded into a hollow mold. Third, the mold halves are then clamped shut and moved into an oven where the loaded mold spins biaxially. In the oven, heat penetrates the mold causing the plastic, if it is powdered form, to become tacky and stick to the mold surface, or if it is liquid form, to start to gel. Heating is done in a gas-fired hot-air oven or similar oven. Because the molds continue to rotate while being heated, the plastics gradually become distributed evenly on the mold cavity walls through gravitational force. As the cycle continues, the polymer melts completely, forming a homogeneous layer of molten plastic. When the parts have been formed, the molds move to a cooling chamber where cooling is accomplished by a cold water spray and/or forced cold air and/or liquid circulating inside the mold. The mold continues to rotate during the cooling cycle so as to ensure that the part does not sag away from the mold surface, causing distortion. The mold is then opened and the parts are removed. This can be done manually or by using forced air or mechanical means to eject the part. Finally, parts can be trimmed, drilled, or cutout to the user""s requirements. Certain tanks require fittings for fill, drain and sensor probes. After fittings are installed, all tanks are pressure/water tested to insure adequate seal.
Examples of patented devices which may be illustrative of such prior art include U.S. Pat. No. 6,143,168 to Shackeford; U.S. Pat. No. 3,909,168 to Greenswell; U.S. Pat. No. 4,343,754 to Wilde et al.; and U.S. Pat. No. 4,680,149 to Rawlings et al.
While these devices may be suitable for the particular purpose to which they address, they are not as suitable for permanent placement of a screen within a plastic structure. Conventional methods of securing a screen within a plastic structure do not provide an adequate long-term securing means.
In these respects, the method of manufacturing a screen device according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of permanent placement of a screen within a plastic structure.
In view of the foregoing disadvantages inherent in the known types of methods of manufacturing and structures now present in the prior art, the present invention provides a new method of manufacturing a screen device construction wherein the same can be utilized for permanent placement of a screen within a plastic structure.
The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new method of manufacturing a screen device that has many of the advantages of the methods of manufacturing mentioned heretofore and many novel features that result in a new method of manufacturing a screen device which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art methods of manufacturing, either alone or in any combination thereof.
To attain this, the present invention generally comprises a screen device includes providing a mold comprised of an upper mold and a lower mold defining a mold cavity, positioning plastic within the mold cavity, positioning a screen upon a lower mold, securing the upper mold to the lower mold with the screen positioned within, performing rotational molding upon the mold, and removing the finished product from the mold. The finished product is comprised of a perimeter structure having an opening within with the screen completely enclosing the opening. The outer perimeter of the screen is molded directly into the inner wall of the finished product to prevent objects from passing about the outside portion of the screen.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and that will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.
A primary object of the present invention is to provide a method of manufacturing a screen device that will overcome the shortcomings of the prior art devices.
A second object is to provide a method of manufacturing a screen device for permanent placement of a screen within a plastic structure.
Another object is to provide a method of manufacturing a screen device utilizing plastic rotational molding.
Another object is to provide a method of manufacturing a screen device that provides an economical means of manufacturing a screen pan structure.
An additional object is to provide a method of manufacturing a screen device that is easy to utilize.
A further object is to provide a method of manufacturing a screen device that provides a complete seal around the exterior portion of the screen.
Another object is to provide a method of manufacturing a screen device that can be utilized upon various sizes of plastic structure.
Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages are within the scope of the present invention.
To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of the appended claims.